DAVIS. — CERTAIN THERMAL PROPERTIES OF STEAM. 



283 



temperature. Inasmuch as nothing is known about that final value 

 of //sat., such an empirical treatment gives no promise of significance. 



In the case of L, on the other hand, one learns from an inspection of 

 figure 8, not only that dL/dt = — oo at the critical point, but also that 

 L = there. This led Thiesen in 1897, 31 to the fortunate suggestion 



400- 



200- 



t 400 



Figure 8. The steam dome on the Ht plane, showing the relationship 

 between the graphs representing the "total heat of saturated steam" and 

 the " heat of the liquid." The former (the upper boundary of the steam 

 dome) is the curve that Regnault believed to be a straight line. It obviously 

 passes a maximum and reaches the critical point with a negatively infinite 

 derivative. 



that if the known values of L at ordinary temperatures can be repre- 

 sented by a formula of the form 



L = A (t c — t) n , n<\, 



one could also be sure that it gave correct values both for L and for 

 dL/dt at the critical point, so that the use of the formula for other high 

 temperatures would be, in a sense, an interpolation rather than an 

 extrapolation. The constants can be determined and the formula 

 tested in the range of the known Z's by writting it in the logarithmic 

 form 



31 Verh. Phys. Gesch., Berlin, 1897, 16, 80. 



